Deasphalting with propane and butane



Jan. 3, 1956 R. H. WAGHORNE ETAL DEASPHALTING WITH PROPANE AND BUTANEFiled June 12, 1952 3 Sheets-Sheet 1 Charles F. Learner 53w attorneg1956 R. H. WAGHORNE arm. 2,729,589

DEASPHALTING WITH PROPANE AND BUTANE 3 Sheets-Sheet 3 Filed June 12,1952 U n h r. e n M a C b N 2 t P( U A 0 r18 n 7 in .M 3 4. E H I m T! wHQ 3 m Iw l 04 D TM I 0 ..mo d C frl 4 W s a B O 0 0 Z a u a m H.

Feed Viscosity, SS0 9 210? N am h r 90 WI. 1: ts n b a o United States 3Claims, (Ci. 196--Il4.46)

This invention concerns a novel process for the deasphalting of residualpetroleum oil fractions to secure high quality lubricating oil stocks.The invention concerns the use of particular proportions of propane andbutane in admixture for treatment of residual oils to eliminateasphaltic and resinous constituents of the oils. By employing adeasphaltiug agent constituting a mixture of propane containing about14% butane, improved deasphalting results are obtained.

in the refining of crude petroleum oils, distillation is commonlyemployed to divide the crude oil into a variety of petroleum fractionssuch as gasoline, kerosene, lubrieating oil, etc. Heavier fractions ofpetroleum oil cannot be successfully segregated by distillationprocedures however. For example, those fractions of petroleum oilboiling above the lubricating oil boiling range or above about 700 .F.are subject to thermal decomposition during distillation even thoughvacuum distillation is employed. To permit the treating and upgrading ofresidual oil fractions, a variety of solvent treating methods arecommonly employed. This invention concerns the solvent treating ofresidual oils in which a low molecular Weight parafiinic hydrocarbon isemployed to precipitate asphaltic and resinous material from theresidual oils to provide valu able lubricating oil blending stocks anddeasphalted stocks variety of other applications.

The residual oils to which this invention has application are theheavier fractions of petroleum oil boiling above 850 F., and containingasphalts and resins. These oils are generally characterized by theirphysical properties rather than their distillation characteristics andgenerally have a specific gravity in the range of about 12.1 to 10.4"APE and viscosities of about 2400 to 6000 SSU at 210 F.

It has been appreciated that parafiinic hydrocarbons are capable ofrejecting or precipitating high molecular weight portions of residualoils including asphalts and resins. It has also been known that as themolecular weight of the precipitating agent is reduced, its solubilityfor asphaltic and resinous compounds is also reduced so as to increasethe precipitating action. For this reason propane is commonly employedas the deasphalting agent in preference to higher molecular weightparaflins such as butane, pentane, etc.

it has now been found however, that inclusion of a critical amount ofbutane in the propane serves to provide an improved deasphalting agent.As will be brought out, use of about 14% of butane in admixture withpropane serves to substantially improve deasphalting results, re-

atent Patented Jan. 53, "less sulting in a higher yield of deasphaltedoil, a deasphalted oil of higher viscosity, a deasphalted oil of bettercolor characteristics at equal volume percent yields, and permitting useof higher asphalt settling temperatures.

The process of this invention and graphical data concerning theinvention are illustrated in the accompanying drawings, in which:

Figure 1 diagrammatically illustrates a deasphalting flow plan which maybe used in the practice of this invention, and;

Figure 2 graphically shows the relation between the viscosity of thedeasphalted oil and the butane content of the solvent, and;

Figure 3 graphically shows the relation between the deasphalted yieldobtainable and the solvent butane content, and finally;

Figure 4 graphically shows the relation between the viscosity of thedeasphalted oil and the feed oil viscosity under conditions of noentrainment and when employing varying proportions of butane in thesolvent.

Referring first to Figure l, a simple diagrammatic flow plan of anoperative solvent deasphalting system is shown. This iiow plan embodiesa system in which multistage mixing and settling of the solvent-residualoil mixture is employed. It is to be understood that the invention mayequally be applied to a countercurrent contacting system in which thesolvent is flowed countercurrently with the residual oil in a contactingtower. In Figure 1 the residual oil feed is introduced to the systemthrough line ll. Deasphalting solvent, primarily constituting a mixtureof propane and butane, is admixed with the oil of stream 1 byintroduction through line 2. This mixture of solvent and oil is passedthrough heat exchanger 3 wherein the mixture is heated to a temperatureof about to 160 F. Recycle solvent obtained through line 4 may be mixedwith the oil solvent mixture together wifla additional solventintroduced through line 5. This mixture of oil teed together with theprimary solvent, secondary solvent, and recycle solvent, is then passedthrough a suitable mixing device such as orifice mixer 6. The thoroughlymixed solvent and oil having a solvent to oil ratio of about 4- to 10 orpreferably about 4 to 6, at a temperature of about 130 to is thenintroduced to a horizontal settling zone 7.

Settler 7 isused to secure a phase separation providing an upper liquidphase consisting of a solvent phase and oil and a lower liquid phaseconsisting of a solvent phase containing precipitated asphaltic andresinous constituents. The upper solvent-oil phase is removed from thesettler through line 8 and is passed through heat exchanger 9 whereinthe oil and solvent mixture is heated to about 135 to F. Recycle solventfrom line 10 is mixed with the oil-solvent mixture and this mixture ispreferably thoroughly mixed in an orifice mixer 11 or the like. Thismixture is then passed to a second settler 12 wherein additional highmolecular weight constituents are settled from the oil. As described,the first settler 7, is primarily effective in secured precipitation ofasphalts while the second settler l2 primarily precipitates resinousmaterials. In settler 12 an upper liquid phase constituting a mixture ofsolvent and deasphalted oil may be removed through line 13 for passageto a deasphalted oil recovery system 14. This system may constitute asteam distillation zone in which steam is employed to stri solvent fromthe deasoh alted oil, permitting removal of the solvent as an overheadstream throu h line 15. The deasphalted oil is then removed as a bottomsproduct through line 16.

The asohaltic phase separating in settler 7 is removed from the lowerportion of the settler throu h line 17 and is mixed with wash solventintroduced through line 18. The wash solvent and asphalt phase are mixedin an orifice mixer 19 and are passed to a settling zone 20. The uppersolvent phase is removed from the upper portion of settler 20 throughline 4 for recycle as described while the precipitated asphalt isremoved from the lower portion of the settler through line 21.

Similarly, the resinous phase of settler 12 is removed from the settlerthrough line 22 and is mixed with wash solvent introduced through line23 by means of orifice mixer 24. This mixture is settled in settler 25permitting removal of solvent through line 10 for recycle as describedand permitting removal of precipitated resins through line 26. Theasphaltic and resinous constituents of lines 21 and 26, together withresidual solvent, are passed to an asphalt recovery system 27 which mayconstitute a fractionation zone. Solvent may be removed overhead throughline 28 and the asphaltic and resinous constituents may be removed as abottoms product through line 29. In the case of asphalt manufacture, alow, viscosity flux oil may be introduced to this system through line 30for admixture with the asphalt removed through line 29.

' In operating a deasphalting system of the character illustrated inFigure 1, in accordance with this invention. the solvent employedconstitutes propane containing about 14% of butane. The discovery thatinclusion of this quantity of butane in the propane is highly desirableresultedfrom basic studies of plant performance. In these studies it wasfound that actual deasphalting plant per.- formance was unaccountablyinferior to apparently equivalent pilot plant performance. Thus, incomparing operating results of a deasphalting plant operating at about4,000 bbls. per day to a pilot plant operating at about 4 bbls. per day,it was found that the yield, color, and viscosity relations of the twosystems showed the plant operation to be greatly inferior. Thisconclusion was established even though the plant and pilot performancewas apparently equivalent. Thus, operations were controlled so thatequal yields of a given viscosity oil were obtained in both the plantand pilot operations, indicating that the two plants provided about thesame stage equivalence. Nevertheless, the color of the refined plant oilwas much darker than the refined pilot unit oil, clearly indicatinginadequate resin and asphaltene removal.

h In studying this anomaly, it was unexpectedly found that there is asharp relation in plant performance between the viscosity of theresidual oil treated, and the molecular weight of the deasphaltingsolvent employed. It was surprisingly found, for example that, contra tothe common understanding, when treating high viscosity residual oils, asolvent having a molecular Weight somewhat greater than propane isparticularly selective. This discovery is opposed to the generalprinciple that no change in selectivity is obtained when varying amolecular weight of the deasphalting agent. Nonetheless, it wasdetermined that greatly improved plant performance may be obtained byincreasing the molecular weight of a propane deasphalting agent byinclusion of butane. Lowering the molecular weight of propanedeasphalting agent by inclusion of methane and'ethane was found to havethe opposite effect, resulting in poorer plant performance. Optimumperformance was found to correspond to a mixture of pure propane withpure butane in which the butane constitutes about 14% of the mixture. Inthe event the solvent also contains small proportions of methane andethane, somewhat greater quantities of butane must be employed.

These differing solvent compositions can best be expressed to compensatefor inclusion of, methane and ethane by definition of the averagemolecular weight of the solvent mixture. Thus, according to thisinvention, a solvent agent is to be employed having a molecular Weightof about 45.8, corresponding to a butane content of about 14%, assumingthat only propane and butane are present.

The basic effect attributable to the use of a solvent agent having amolecular weight of about 45.8 is apparently related to the entrainmentcharacteristics of a residual oildeasphalting solvent mixture. pilotplant tests referred to there was no entrainment of asphalt in thedeasphalting solvent after phase separation. However, in plantoperations, due to the impracticality of securing equivalent settling ina plant, substantial asphalt entrainment in the deasphalted oilordinarily occurs. For some reason, increasing the molecular weight ofthe deasphalting solvent by inclusion of butane in the propanedeasphalting agent serves to correct this condition, permitting completeelimination of entrainment under plant conditions when 14% of butane ismixed with propane. This is illustrated in Figure 2 of the drawingsshowing the relation between the viscosity of deasphalted oil of aconstant color and the butane content of a propane-butane solventmixture used for deasphalting. The feed oil had a viscosity of 3000 SSUat 210 F. In plant operations using pure propane, due to entrainment ofasphalt, the deasphalted oil was found to have a viscosity of about 195.Inclusions of small percentages of butane in the propane serve tominimize this entrainment, but about 14% of butane was found to berequired in order to completely eliminate asphalt entrainment in thedeasphalted oil.

This same relation was established by reference to the yield ofdeasphalted oil of a constant color as compared to the butane content ofthe solvent. This is illustrated in Figure 3 wherein it is shown thatgreatly improved yields of deasphalted oil are obtained as entrainmentof asphalt is eliminated by increasing the butane content of thesolvent. Again the optimum yield of deasphalted oil is obtainable by theelimination of asphalt entrainment obtained by using a deasphaltingagent containing about 14% of butane.

While the advantages of using 14% of butane in admixture with propaneare clearly related to elimination of asphalt entrainment as described,the basic reason for this phenomenon is not now known. In the graphs ofFigures 2 and 3, it is apparent that greater deasphalted oil yields areobtainable for oils of the same color char acteristics since eliminationof entrainment of asphalts provides better color characteristics athigher yield levels. Similarly, better precipitation of asphalt permitsmore selective elimination of higher molecular weight constituents so asto enable obtaining an oil product of higher viscosity. It is presentlybelieved that these effects are probably due to an increased asphaltphase particle size. It is also probable that an increased interphasegravity differential obtainable by inclusion of butane contributes tothis effect. In any case, as presented, it has been established that apropane-butane mixture containing about 14% butane is a particularlydesirable deasphalting agent. As emphasized, the nature of this agentmay be expressed by the average molecular weight of the agent which mustbe about 45.8.

To exemplify the nature and benefits of this invention, a series of testruns were made in an actual deasphalting plant in which the molecularWeight of the solvent composition was varied by inclusion of butane in asolvent consisting predominantly of propane. Each of the runs were madeto provide a deasphalted oil having a constant color while determiningthe yield and viscosity of deasphalted oil obtainable. These tests arefully presented in Table I, showing the operating variables and thedeasphaltedoil characteristics.

It was found that in the assesso- TABLE 1 Plant test data showing efiectof varying solvent butane content and deasphalted oil color Run N0. 1 23 4 6 Feed Rate, BJSD 3,737 3, 814 3, 814 3, 836 3,938 Feed Viscosity,SSU 210 Fm.v 2, 990 3, 010 3, 003 3,060 3, 990 Deaspholted Oil:

Rate, BJSD 1, 610 1, 707 1, 795 1, 31s 1, 818

Yield, Vol. percent 43. 44. 8 7. 1 47. 4 40. 2 Viscosity. SSU 210 F. 203209 220 223 234 Color, TR Dil 1 1 1 1 3/4 Solvent/Feed Ratios, Vol/Vol.

Feed:

Primary 1 0. 77 0. 0. 76 0. 70 0. 94

Secondary... 0. 70 0. 76 0. 78 0. 68 0. 63

Asphalt Wash- 1. 12 1.15 1.16 0.97 1.40

Resin Wash.-- 1. 22 1. 22 1. 22 1. 19 1. 36

Tot 3.90 3.89 3 92 3.53 4 33 Settler Temperatures, F.:

Asphalt 132 138 146 149 Resin 140 149 149. 5

Asphalt Wash. 103 102 103 115 115 Resin Wash 114 115 116 121 124 SolventComposition Avg. Mol. Wt 44. 61 44. 96 45. 48 45. 77 46. 06

Cale. Butane Content, Vol.

Percent 4. 3 7. 2 ll. 4 13.8 15. 8

Calculated from mass spectrometer analysis and simple flash vaporizationtest results.

b Calculated from average molecular Weight assuming only Ca and C4greent. Methane content ranged from 0.0 to 0.3%; ethane from 0.3 to

Referring to Table I, it will be observed that in increasing the butanecontent from 4.3% to 13.8% in the successive runs 1, 2, 3 and 4, thevolume percent yield of deasphalted oil was progressively increased from43% to 47.4%. Similarly, the viscosity of the deasphalted oil wassubstantially increased by increasing the butane coutcnt of thedeasphalting solvent. Run No. 5 employing even higher butane contents inthe solvent is not strictly comparable to runsl to 4 since an oil ofsomewhat poorer color was obtained. Comparison of the yield andviscosity results however shows that substantially no improvement wasobtained by using the higher percentage of butane.

This conclusion was verified by carefully controlled tests in which thebutane content of the solvent was increased above 14%. Again theexperiments conducted were in an actual dcasphalting plant. The resultsof these experiments are fully given in Table ll:

TABLE 11 Plant test data showing effect of varying solvent bur mecontent and deasphalted oil color Run N0. 1 2 3 Feed Rate, BJSD .1 3,711 3, 748 3, 728 Feed Viscosity, SSU 210 F 2, 530 2, 450 2, 400Deasphalted 01']:

Rate, B./SD 1, 807 1, 812 1. 792 Yield, Vol. Percent 48. 7 48. 3 48. 1Viscosity, SSU 210 F 199 202 199 Color TR Dil 3/4 3/4 3/4 SolventRatios, Vol/Vol. Feed:

Primary 1. 02 1. 01 1. 01 Secondary 0 88 0. 87 0 87 Asphalt Wash 1 56 1.58 1 70 Resin Wash 1 67 1.67 1 07 Total 5 13 5.13 5 25 Settler TempeAsph t 147 154 161 Resin 147 155 161 Asphalt Wash 112 112 114 Resin Wash126 138 142 Solvent Composition:

1 Avg. Molecular Wt. 45. 75 46. 60 47. 2 Cole. Butane Content, Vol.Percent a-.- 13.8 20. 0 24. 0

It will be observed from the data of Table II that the yield andviscosity of deasphalted oil of comparable color were not improved byincreasing the molecular weight of the solvent above about 45.8 or byincluding more than about 14% of butanein the solvent. This datatogether withthe data of Table I therefore establishes that inclusion ofabout 14% of butane in a propane deasphalting solvent is criticallyeffective in eliminating entrainment of asphalt permitting higher oilyields, better viscosity, etc. In considering the possibility ofemploying higher percentages of butane, it is necessary to appreciatethat butane recovery cannot be accomplished with the efiiciency ofpropane recovery. Thus, butane is selectively lost in the typicalsolvent recovery facilities of a deasphalting plant. Consequently, it isextremely undesirable to employ more than 14% of butane in thedeasphalting solvent. It is for this reason that the amount of butane tobe employed is critically set at about 14% and no more and no less thanthis proportion of butane is to be employed.

in studying the improvement in dcasphalting results obtained by addingbutane to a propane deasphalting agent, it was also found that highersettler temperatures could be employed when butane was included. Thus,in a typical case, in order to obtain a dcasphalted oil of suitablecolor characteristics, it was found that a settler temperature of about133 F. was required when using pure propane. However, when 14% of butanewas included with the propane it was found. that a settler temperatureof 148 F. could be employed to obtain deasphalted oil of equal quality.This again is an important advantage, of using the butane-propanemixture as a deasphalting agent. This is particularly important in warmclimates or in areas where adequate cooling Water is not available,since the temperature which may be maintained in the settler of adeasphahing plant is frequently a limiting process variable.

Further experiments with the dcasphalting agent of this inventionestablished that the improvements referred to are primarily obtained inthe treatment of high viscosity residual oils. Thus, inclusion of butanein a propane solvent has little effect in improving deasphalting of. alow viscosity residual oil. However, when the residual oil has aviscosity above about 2500 SSU, the full benefits of this invention maybe obtained. Preferably the invention is employed for the treatment ofresidual oils having a viscosity above 3,000 SSU at 210 F. This isillustrated by Figure 4 of the drawings showing the relation between theviscosity of deasphalterl oil and the feed viscosity. Referring toFigure 4 graphical line A shows the relation of deasphalted oilviscosity to feed oil viscosity in pilot plant operations underconditions wherein there was no entrainment of asphalt in thedeasphalted oiI. Line B shows the plant results obtainable when using atleast 13% of butane in the solvent while line C shows the plant resultsobtainable when no butane was included in the solvent. It will beobserved that below a feed viscosity of about 2500 little improve mentin deasphalting results were obtained by inclusion of the butane.However, particularly above feed viscosiiies of 3,000, inclusion of 13%butane or more permitted obtaining results substantially equivalent tono entrainment conditions. it must be appreciated therefore that theprocess of this invention is primarily adapted to the treatment ofresidual oils having a viscosity above about 3,000 SSU at 210 F. Inconsider-sing the benefits of this invention it is important to note theadvantages of obtaining a higher viscosity deasphalted oil thanotherwise obtainable. Thus, as emphasized, by using the deasphaltingagent of this invention including 14% of butane, a dcasphalted oilviscosity increase of as much as 30 units may be obtained. This servesto further magnify the increases in dcasphalted oill yields since thehigher viscosity deasphalted oil can be blended with greater amounts oflow viscosity lubricating oil blending stocks, thereby under comparableconditions, an increase in lubricating oil production of as much as 27%can practically be obtained.

What is claimed is:

1. A ,deasphalting process in which a residual oil having a viscosityabove about 2500 S. S. U. at 210 F. is admixed with a deasphalting agentconsisting essentially of propane and butane in which the said butanecornprises about 14% by volume of the deasphalting agent.

2. A multi-stage deasphalting process which comprises contacting aresidual oil having a viscosity above about 3000 S. S. U. at 210 F. andcontaining asphaltic and resinous constituents with a. deasphaltingagent consisting of a C1 to C4 paraffinic hydrocarbon mixture having anaverage molecular weight of about 45.8.

'3. The process of claim 2 wherein the reaction mixture References Citedin the file of this patent UNITED STATES PATENTS Bray Jan. 23, HaylettJuly 31, Frolich May 3, Bahlke et al. Feb. 7,

Adams Mar. 5,

ituents and parafiinic at a tem

1. A DESAPHALTING PROCESS IN WHICH A RESIDUAL OIL HAVING A VISCOSITYABOVE ABOUT 2500 S.S.U. AT 210* F. IS ADMIXED WITH A DEASPHALTING AGENTCONSISTING ESSENTIALLY OF PROPANE AND BUTANE IN WHICH THE SAID BUTANECOMPRISES ABOUT 14% BY VOLUME OF THE DESAPHALTING AGENT.